This invention relates generally to screen printing and, more particularly, to an adhesive tape used to seal printing screen from ink penetration.
Silk-screen printing, more accurately designated "screen printing", has long been used to produce high quality illustrations although its method does not readily lend itself to high volume production. In the last decade, however, screen printing has had a resurgence in use for applications where long runs of high quality prints are desired, this resurgence being due to the use and the process of more complex, automatic equipment.
Screen printing is a form of stencil printing using a design fashioned from an emulsion or other material attached to a woven sheet of fabric (silk, organdy, nylon or polyester fibers, copper, stainless steel strands, etc.) which has been tightly stretched across a frame. Ink is then forced through the open meshes of the fabric sheets by means of a rubber blade or squeegee. The size of the opening in the mesh of the woven fabric, if formed of silk might vary from 6XX (coarse) to 18XX (very fine). The mesh can also be achieved by etching a thin metal plate but more commonly is formed by a woven fabric.
Pervading all screen printing applications, particularly where a flexible fabric is used, is the requirement that certain screen area, generally that residing from a stencil's outside edge to the screen's frame, be sealed from ink penetration. This seal is needed to prevent ink from leaking around the stencil's outside edge to bleed onto the object being printed. Typically, adhesive tape is used as a sealant.
A split tape, popularly used today, has a release liner covering the tape's adhesive side. The liner is scored lengthwise down the tape's approximate center. Aided by the scoring, an operator peels one-half of the release liner away from the tape's adhesive and leaves the other half of release liner in place. The operator then places the half with exposed adhesive directly onto the screen and allows the half still covered by the release liner to simply rest against the sides of the screen-printing frame.
There are problems with this tape and its associated split liner. Excessive ink can flow behind the tape, between the tape and the frame, because this half of the split tape is not adhered to the frame. Such may allow ink to flow through the screen to ultimately bleed over the printed image underneath. Or possibly worse, this half of split tape may fall inward and onto the screen which may allow even more bleeding.
Additional problems relate to the use of a liner. The operator must peel away this liner before applying the tape. This added step slows down production and creates additional waste. And occasionally, the process of scoring the release liner damages the tape. If scored too deep, the tape is cut and any seal the tape might form is breached. Because of these problems and the respective higher cost of this tape, conventional tapes such as mastic tape or duct tape have been tried as well.
As most frames are made of aluminium, adhesives tend to grab aggressively to the frame and leave behind adhesive residue when the tape is removed. If masking tape is used, it generally will not pull off in one piece but will tear into many small strips. The additional labor cost to pick off the many small pieces makes it an expensive process. Additionally, adhesive residue is left behind on the frame and screen. If duct tape is used, the strips usually come off in one piece, but much adhesive is left behind upon the frame and screen. The operator must either leave the adhesive on the expensive frame for further build up, or use solvents to scrub the frame clean, a very labor intensive and expensive process.
With these thoughts in mind, an improved sealing tape for screen printing is needed which combines the production efficiency of linerless tape without the problems created by adhesive residue upon its removal. Preferably, the tape would be cheaper than existing release liner tapes and leave little to no adhesive behind after its use.